唯我独尊
1
throughout heaven and earth, I alone am the honored one
See also:
天上天下唯我独尊 (てんじょうてんげゆいがどくそん)
本人は唯我独尊を決め込んでいるようだけども、周りから見れば単なるわがままだよね。
He's completely convinced of his own greatness but to the people around him he's just a selfish jerk.
2
self-conceit;self-centeredness;vainglory